hehe, Mate..
I design icons too
working on a project..
I have win XP and tried to make one sample
of icon, it's original res is 300x300 and using IconoMaker convrted size to 48 and when I use it as windows folder icon or just use it , it does not look nice any tips?

hmm, i am a beginner in this icon field, in fact this is the very first icon i have ever made. However, my spontaneous tip for u is to change the resolution inside of photoshop or whatever image software you are using instead of letting the icon program make it for you.